9 



In Ontario County and the Genesee Valley, this shale has a nuich 

 greater thickness, amounting, according to Hall* to about 150 feet in 

 Ontario County. Correspondingly we find a richer fauna, sixtA'-six 

 species hax-ing been recorded by Clarke in 1885. t The fauna is rich 

 in Goniatites, and as Clarke has shown, recalls the characteristic 

 association of fossils found in the " Inttimescens " beds of the lower 

 Upper Devonian of the continent of Europe. It is therefore regarded as 

 representing the transatlantic development of the European " Intu- 

 mcscens faima." (See J. M. Clarke — "The fauna wnth Goniatites 

 intnmescens (Beyr.) in Western New York." Am. Geol., Vol.VIII, p. 86.) 



The Black Genesee Shales.— These shales recall the bitti- 

 mirious Naples shales, the latter representing a recurrence of 

 the conditions under which the bituminous Genesee shales 

 were deposited. These shales are fissile when Aveathered, 

 but appear heavy bedded in the fresh mass. Pyrite in 

 minute disseminated grains, and in larger concretionary 

 masses is very common, and from its oxidation, the surfaces 

 of the weathered shale laminae are covered with a coating 

 of red and brown iron rust. There are, however, no large 

 calcareous concretions, such as are common in the black 

 shales above. The jointing is very perfect, and frequently 

 blocks produced by the intersection of the joints, project 

 from the wall, ready to fall. The joint faces are often 

 thickly covered with an efflorescence of alumn. 



The oxidation of the pyrite furnishes free sulphuric acid, which, if in 

 excess, will attack the shale and form aluminium sulphate and silica. 

 The reactions may be v^ritten : 



a. 2 Fe S,+7 0,+2 Y{.fi=^2 Fe SO^-f 2H2 SO4. 



h. 6 H,S04+Al,(Si 0:j), Al,05H^:i:-^2 Al,(Si 0^3+3 Si 0,+8 H.O. 



The aluminium sulphate will crystallize in dry places. 



Fossils are rare in these beds and consist mainl}^ of the 

 characteristic Genesee species, viz: Lunulicardium fragile 

 (Hall) and Stvliolina £ssurella (Hall). 



The Gray Genesee Shales. — These consist in descending 

 order of: 



*Geol. N. Y. Rep't, 4th Geol. Dist., 184-3, p. 221. 



fBull, 16 U.S. Geol. Survey. The mitnber of species has been added to since then. 



|The approxiniat<; formula for clay slate. 



